The invention is directed to a control device for a supplementary air valve operative in accordance with temperature and time. A control device is disclosed in U.S. Pat. No. 4,294,217 in which a bimetallic element is disposed within a housing in a socket of die-cast plastic. This construction has the disadvantage that plastic tends to deteriorate with time, which can lead to an unplanned shift in the position of the bimetallic element within the housing, resulting in a potential for change in the behavior of the control device.